Ultrasonic probe

ABSTRACT

An ultrasonic probe is provided which may be employed in medical applications to radiate an ultrasonic wave for inspecting the interior of a patient&#39;s body noninvasively. The ultrasonic probe includes a scan mechanism which consists of a rotating mechanism and a swinging mechanism. The rotating mechanism is designed to rotate a cylindrical holder having installed thereon a piezoelectric element which emits an ultrasonic wave and receives the echo. The swinging mechanism is designed to swing a rotary base which supports the rotating mechanism to swing the cylindrical holder about an axis of rotation extending perpendicular to that of the piezoelectric element.

BACKGROUND OF THE INVENTION

1. Technical Field of the Invention

The present invention relates generally to an ultrasonic probe which isused in, for example, medical applications to radiate an ultrasonic wavefor inspecting the interior of a patient's body noninvasively, and moreparticularly to an improved structure of a scan mechanism of anultrasonic probe designed to rotate a piezoelectric element emitting theultrasonic wave.

2. Background Art

Japanese Patent First Publication No. 5-337108 teaches a scan mechanismfor an ultrasonic probe. The scan mechanism includes a rotor having apiezoelectric element installed thereon and two electric motors one ofwhich rotates the piezoelectric element about a first axis and other ofwhich swings the piezoelectric element about a second axis perpendicularto the first axis.

The scan mechanism is, however, complex and bulky in structure andencounters the drawback in that it is difficult to use the ultrasonicprobe in a small cavity of a person's body, for example.

SUMMARY OF THE INVENTION

It is therefore a principal object of the present invention to avoid thedisadvantages of the prior art.

It is another object of the present invention to provide a simple,lightweight, and inexpensive structure of a scan mechanism of anultrasonic probe designed to rotate a piezoelectric element emitting anultrasonic wave.

According to one aspect of the invention, there is provided anultrasonic probe which comprises: (a) a piezoelectric element emittingan ultrasonic wave and receiving an echo thereof, the piezoelectricelement converting the echo into an electric signal; (b) a holdingmember holding the piezoelectric element; (c) a rotating mechanismrotating the holding member about a first axis; (d) a rotary basesupporting the rotating mechanism; (e) a chassis supporting the rotarybase so as to allow the rotary base to swing about a second axisextending in a direction different from the first axis; and (f) aswinging mechanism swinging the rotary base.

In the preferred mode of the invention, the rotating mechanism includesa holding member angular position measuring encoder designed to measurean angular position of the holding member.

The holding member angular position measuring encoder may include afirst encoder unit and a second encoder unit each of which is made of amagnetic member and a magnetoresistive element. The first encoder unitis designed to measure a change in angular position of the holdingmember by rotation about the first axis. The second encoder unit isdesigned to measure a preselected reference angular position of theholding member.

The rotating mechanism includes a holding member rotating electric motorrotating the holding member made of a rotary cylinder, a conductivecylinder arranged in alignment of a central axis with a central axis ofthe rotary cylinder, and a conductive brush installed on the rotary basein contact with the conductive cylinder.

The rotating mechanism may alternatively include a holding memberrotating electric motor rotating the holding member made of a rotarycylinder, a first coil installed on the rotary cylinder, and a secondcoil installed on the rotary base so as to face the first coil. Thefirst coil is responsive to a change in magnetic flux of the second coilto produce an electric signal for energizing the piezoelectric element.

The swinging mechanism includes a rotary base swinging electric motor,an motor angular position measuring encoder measuring an angularposition of the rotary base swinging electric motor, and a gear traintransmitting output torque of the rotary base swinging electric motor tothe rotary base to swing the rotary base.

The swinging mechanism may alternatively include a voice coil motor anda rotary base angular position measuring encoder which measures anangular position of the rotary base. The voice coil motor is implementedby a magnet installed on one of the rotary base and the chassis and anelectric coil installed on the other of the rotary base and the chassis.

A holding mechanism may also be provided which is designed to hold therotary base on the chassis.

A second piezoelectric element may further be installed on the holdingmember which produces an ultrasonic wave having the same frequency ofthat produced by the piezoelectric element.

The second piezoelectric element may alternatively be designed toproduce an ultrasonic wave having a frequency different from thatproduced by the piezoelectric element.

A magnetoresistive element may also be provided which is responsive to achange in magnetic flux produced by the magnetic member of the secondencoder to provide a signal indicative of a neutral position of theholding member in swinging motion of the holding member.

An array of magnetoresistive elements may also be installed on thechassis. Each of the magnetoresistive elements is responsive to a changein magnetic flux produced by the magnetic member of the second encoderto provide a signal indicative thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be understood more fully from the detaileddescription given hereinbelow and from the accompanying drawings of thepreferred embodiments of the invention, which, however, should not betaken to limit the invention to the specific embodiments but are for thepurpose of explanation and understanding only.

In the drawings:

FIG. 1 a cutaway perspective view which shows an ultrasonic probeaccording to the first embodiment of the invention;

FIG. 2 is a perspective view which shows a rotor motor installed in theultrasonic probe of FIG. 1;

FIG. 3(a) is a side view which shows a side of the rotor motor of FIG.2;

FIG. 3(b) is a side view which shows a side of the rotor motor opposedto FIG. 3(a);

FIG. 4 is a sectional view which shows an internal structure of therotor motor of FIG. 2;

FIG. 5 is an illustration which shows output signals from an encodermeasuring an angular position of a piezoelectric element;

FIG. 6 is a perspective view which shows a rotor motor according to thesecond embodiment of the invention;

FIG. 7 is a perspective view which shows a rotor motor according to thethird embodiment of the invention;

FIG. 8(a) is a partially sectional view which shows a lock mechanismused in the rotor motor of FIG. 7;

FIG. 8(b) is a partially sectional view which shows a side of the lockmechanism opposed to FIG. 8(a);

FIG. 9 is a partially sectional view which shows a rotor motor accordingto the fourth embodiment of the invention;

FIG. 10 is a partially sectional view which shows a rotor motoraccording to the fifth embodiment of the invention;

FIG. 11 is an illustration which shows a measurement range of anultrasonic probe of the fifth embodiment of the invention;

FIG. 12 is a perspective view which shows a rotor motor according to thesixth embodiment of the invention;

FIGS. 13(a) and 13(b) show waveforms of signals outputted from anencoder in the sixth embodiment of the invention;

FIG. 14 is a perspective view which shows a rotor motor according to theseventh embodiment of the invention; and

FIGS. 15(a) and, 15(b) and 15(c) show waveforms of signals outputtedfrom an encoder in the seventh embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings, wherein like numbers refer to like partsin several views, particularly to FIG. 1, there is shown an ultrasonicprobe 1 according to the first embodiment of the invention which may beemployed in an ultrasonic diagnostic system designed to view theinterior of a patient noninvasively.

The ultrasonic probe 1 includes a rotor motor 2, an electric signaltransmitting wire 3, a drive shaft 4, a second encoder 170 (a firstencoder will be described later), a second electric motor 160 (a firstelectric motor will be described later), a motor bracket 15, flexiblejoint 14, a pipe 5, a joint frame 6, a housing 7, a shaft holder 16, awindow 8, and an oil seal 9.

The rotor motor 2 works to scan an ultrasonic wave. The second electricmotor 160 rotates the drive shaft 4. The second encoder 170 measures arotational angle of the drive shaft 4. The motor bracket 15 supports thesecond electric motor 160. The flexible joint 14 transmits the torqueoutput of an output shaft of the second electric motor 160 to the driveshaft 4. The pipe 5 retains the rotor motor 2 and covers the drive shaft4. The joint frame 6 supports the pipe 5. The housing 7 is fixed on thejoint frame 6. The shaft holder 16 is fixed on the joint frame 6. Thewindow 8 covers the rotor motor 2 and outputs the ultrasonic wavetherethrough.

The inside of the window 8 is filled with a coupling liquid 10 in whichthe degree of attenuation of the ultrasonic wave is low. The oil sealavoids leakage of the coupling liquid 10 from a clearance between thedrive shaft 4 and the pipe 5. For the brevity of illustration, thewindow 8, the shaft holder 16, the housing 7, the joint frame 6,and thepipe 5 are partially cut away in FIG. 1.

FIG. 2 shows the structure of the rotor motor 2. For the convenience ofillustration, a chassis 11 is partially cut away.

The rotor motor 2 includes the first electric motor 110. The firstelectric motor 110 has an outer cylinder 111 on which magnetic members121 and 122 are installed. The magnetic member 121 is, as will bedescribed later in detail, magnetized to have a given magnetic patternfor measuring an angular change of the outer cylinder 111. The magneticmember 122 is magnetized for determining a reference angular position ofthe outer cylinder 111. The outer cylinder 111 has formed thereon amount 118 for mounting a piezoelectric element 130 and installed thereona conductive cylinder 150 in alignment of the center thereof with anaxis of rotation of the outer cylinder 111. The rotor motor 2 alsoincludes a rotary base 140 which has formed therein a hole 141 forholding a central axis of the first electric motor 110 and installedthereon a magnetoresistive element 123 (i.e., a magnetroresistor)sensitive to a change in magnetic flux of the magnetic member 121 of thefirst encoder 120, a magnetoresistive element 124 sensitive to a changein magnetic flux of the magnetic member 122 of the first encoder 120, aconductive brush 151, and a first spur gear 142. On the chassis 11, asecond spur gear 143 and a first bevel gear 144, as shown in FIGS. 3(a)and 3(b) are installed rotatably. The second spur gear 143 meshes withthe first spur gear 142. The first bevel gear 144 is arranged coaxiallywith the second spur gear 143 and meshes with a second bevel gear 145coupled to the drive shaft 4. The rotary base 140 has formed thereonarc-shaped protrusions or rails 146 and 147 which have a trapezoidalsection and slidably engage grooves 12 and 13 formed in the chassis 11to support the rotary base 140 so that it may swing.

Internally, the first electric motor 110, as shown in a sectional viewof FIG. 4, includes an electric coil 112, permanent magnets 113 and 114, a central shaft 115, and bearings 116 and 117. The electric coil 112is attached to the central shaft 115. The bearings 116 and 117 supportsthe outer cylinder 111 rotatably on the central shaft 115. The permanentmagnets 113 and 114 are installed in the outer cylinder 111.

FIG. 5 shows the waveform of signals outputted by the first encoder 120.The first encoder 120, as described above, consists of a first encoderunit designed to measure an angular change of the outer cylinder 111caused by rotation of the outer cylinder 111 and a second encoder unitdesigned to detecting the reference angular position of the outercylinder 111. The first encoder unit is made of the magnetic member 121and the magnetoresistive element 123 which is sensitive to the magneticpattern provided on the magnetic member 121 to produce electric signals,as discussed below. Similarly, the second encoder unit is made of themagnetic member 122 and the magnetoresistive element 124 which ismagnetically responsive to the magnetic member 122 to produce anelectric signal as discussed below. Specifically, the first encoder 120,as clearly shown in the drawing, outputs three signals: angular signals181 and 182 and a reference angular signal 183. When the outer cylinder111 is rotated about the central shaft 115, it will cause the angularsignals 181 and 182 to change in level cyclically as shown in thedrawing. A phase difference between the angular signals 181 and 182indicates the direction of rotation of the outer cylinder 111. Thenumber of pulses of each of the angular signals 181 and 182 represents achange in angular position of the outer cylinder 111. The referenceangular signal 183 is produced whenever the second encoder unit reachesa preselected reference angular position, that is, whenever the magneticmember 122 passes the magnetoresistive element 124. The first encoder120 resets the measured angular change of the outer cylinder 111whenever the reference angular signal 183 is detected. In FIG. 5, thesignals 181, 182, and 183 are illustrated as having different signallevels for convenience, however, these signal levels are, in fact,identical with each other.

In operation, an electric signal produced by an ultrasonic diagnosticsystem (not shown) is inputted in the form of a pulse signal to theconductive brush 151 installed on the rotary base 140 of the rotor motor2 through the wire 3. The conductive brush 151 is in contact with theconductive cylinder 150 installed on the outer cylinder 111, so that theelectric signal inputted to the conductive brush 151 is transmitted tothe conductive cylinder 150. The conductive cylinder 150, although notshown in the drawings, is electrically connected to the piezoelectricelement 130, so that the electric signal inputted to the conductivecylinder 150 is further transmitted to the piezoelectric element 130.The piezoelectric element 130 converts the inputted electric signal intooscillations to produce an ultrasonic wave and radiates it to theoutside. If there is a reflective object in a propagation path of theultrasonic wave, the ultrasonic wave is returned to the piezoelectricelement 130. The piezoelectric element 130 converts the echo of theultrasonic wave into an electric signal and outputs it to the ultrasonicdiagnostic system through the conductive brush 151, the conductivecylinder 150, and the wire 130. The ultrasonic diagnostic systemconverts the input signal into an image signal using known imagingtechniques.

During the radiation, the ultrasonic wave is scanned over 360° toproduce an ultrasonic tomogram (i.e., an ultrasonogram) of the object.The scanning is achieved by energizing the electric coil 112 of thefirst electric motor 110 to rotate the outer cylinder 111 about thecentral shaft 115 (i.e., the x-axis in FIG. 2), thereby rotating thepiezoelectric element 130. The angular position of the outer cylinder111 is measured by the first encoder 120 to provide an angular positionsignal to the ultrasonic diagnostic system as indicating the position ofa scanned portion of the object on the ultrasonic tomogram.

When it is required to shift the radiation of the ultrasonic wave (i.e.,the scanned area of the object) in a direction perpendicular to therotation of the outer cylinder 111, the second electric motor 160 isactuated to provide torque to the second bevel gear 145 through thedrive shaft 4. The torque is subsequently transmitted to the first bevelgear 144 and to the first spur bear 142 through the second spur gear143. The first spur gear 142 is installed on the rotary base 140, sothat the rotary base 140 swings about the x-axis extending, as shown inFIG. 2, perpendicular to the y-axis along guide paths defined byslidable engagement of the rails 146 and 147 with the grooves 12 and 13formed in the chassis 11. The angular position of the drive shaft 4 ismeasured by the second encoder 170 to provide an angular position signalto the ultrasonic diagnostic system as indicating the angular positionof the rotary base 140 on the guide path.

As apparent from the above discussion, the first embodiment of theinvention provides a simple and small-sized structure of the rotor motor2 to enable the ultrasonic probe 1 to be constructed which is capable ofproducing an ultrasonic monogram of an object and measures the angularposition of the head of the probe 1 with high and confidence levels.

FIG. 6 shows a rotor motor 2A according to the second embodiment of theinvention. The same reference numbers as employed in the firstembodiment refer to the same parts, and explanation thereof in detailwill be omitted here.

The rotor motor 2A is different from the rotor motor 2 of the firstembodiment only in that the outer cylinder 111 has installed thereon thefirst coil 200 connected to the piezoelectric element 130, and therotary base 140 has installed thereon the second coil 201 facing thefirst coil 200 with a given gap.

In operation, the ultrasonic diagnostic system provides a pulse signalof 80V to 200V to the second coil 201 through the wire 3. This causesthe magnetic flux of the second coil 201 to be changed suddenly, therebyresulting in production of voltage at the first coil 200. The first coil200 is, as described above, connected to the piezoelectric element 130,so that the voltage produced at the first coil 200 is applied to thepiezoelectric element 130, thereby causing pulses to be radiated in theform of an ultrasonic wave. When the echo of the ultrasonic wave reachesthe piezoelectric element 130, the piezoelectric element 130 convertsthe input into an electric signal in the form of a pulse signal outputsit to the first coil 200, so that the magnetic flux thereof is changedsuddenly, thereby causing the second coil 201 to produce the voltage.The voltage is transmitted to the ultrasonic diagnostic system throughthe wire 3 and converted into an image signal.

The rotor motor 2A of this embodiment is, as apparent from the above,designed to establish signal transmission between a rotary member and astationary member without mechanical sliding motion, thereby reducingthe wear of parts of the ultrasonic probe.

FIG. 7 shows a rotor motor 2B according to the third embodiment of theinvention. The same reference numbers as employed in the firstembodiment refer to the same parts, and explanation thereof in detailwill be omitted here.

The rotary base 140, like the first embodiment, has formed thereon thearc-shaped rails 146 and 147 which engage, as shown in FIGS. 8(a) and8(b), the grooves 12 and 13 formed in the chassis 11 slidably. Therotary base 140 has a magnet 210 installed thereon. The chassis 11 hasinstalled thereon an electric coil 211 which forms a voice coil motortogether with the magnet 210. The rotary base 140 has disposed thereon amagnetic member 222 magnetized to have a given magnetic pattern. Thechassis 11 has disposed thereon a magnetoresistive element 224 which issensitive to a change in magnetic field produced by the magnetic member222. The rotary base 140 has also installed thereon a magnetic member(not shown) which is identical with the magnetic member 222. The chassis11 has also installed thereon a magnetoresistive element (not shown)which is identical with the magnetoresistive element 224 and whichmeasures a preselected neutral position of the rotary base 140 in theswing thereof in the same manner as that of the first encoder 120 in thefirst embodiment. These magnetic members and magnetoresistive elementsform a swing angle measuring encoder. The rotary base 140 has, as shownin FIGS. 8(a) and 8(b), formed therein a hole 148 into which a lever 301is inserted to hold he rotary base 140 in the chassis 11 fixedly. Thelever 301 is urged by a coil spring 302 into constant engagement withthe hole 148 and moved out of the engagement by a solenoid 300.

In operation, when the solenoid 300 is energized, it will cause thelever 301 to be attracted downward, as viewed in FIGS. 8(a) and 8(b),into disengagement from the hole 148, thereby allowing the rotary base140 to rotate.

Subsequently, when the coil 211 disposed within a magnetic fieldproduced by the magnet 210 is energized, it produces a magnetic force.The coil 211 is fixed on the chassis 11, so that a reactive force isproduced which swings the rotary base 140 along the guide , pathsdefined by the rails 146 and 147 formed on the rotary base 140 and thegrooves 12 and 13 formed in the chassis 11. The angular position of therotary base 140 changed by the swing is measured by the swing anglemeasuring encoder. When it is required to hold the rotary base 140 fromswinging, the solenoid 300 is reenergized to urge the lever 301 intoengagement with the hole 148 in the rotary base 140 with aid of thespring load of the coil spring 302 to lock the rotary base 140.

The structure of the third embodiment is designed to swing the rotarybase 140 without use of a gear train as employed in the secondembodiment, thereby minimizing the wear of parts working to swing therotary base 140. Further, when not in use, the lever 301 is fittedwithin the hole 148 formed in the rotary base 140 to lock the rotarybase 140, thereby avoiding undesirable movement of the rotary base 140during transportation of the ultrasonic probe, for example.

The electric coil 211 and the magnet 210 may alternatively be disposedon the chassis 11 and the rotary base 140, respectively.

FIG. 9 shows a rotor motor 2C according to the fourth embodiment of theinvention which is different from the rotor motor 2 of the firstembodiment only in that two piezoelectric elements 130 and 131 areinstalled on the outer cylinder 111 which produce oscillations at thesame frequency. Other arrangements are identical, and explanationthereof in detail will be omitted here.

The rotor motor 2C may also use more than two piezoelectric elements forspeeding up the acquisition of ultrasonograms.

FIG. 10 shows a rotor motor 2D according to the fifth embodiment of theinvention which is different from the rotor motor 2 of the firstembodiment only in that two piezoelectric elements 130 and 132 areinstalled on the outer cylinder 111 which produce oscillations atdifferent frequencies. Other arrangements are identical, and explanationthereof in detail will be omitted here.

When the ultrasonic wave passes through an object, as the frequency ofthe ultrasonic wave increases, the resolution becomes fine, but thedegree of attenuation increases. Therefore, the use of ultrasonic wavehaving a higher frequency, enables acquisition of a finer ultrasonogram,but the distance to an object which allows an ultrasonogram to be formeddecreases. Conversely, the use of ultrasonic wave having a lowerfrequency results in an increase in distance to an object which allowsan ultrasonogram to be formed, but the resolution of the ultrasonogramdecreases. The rotor motor 2D of this embodiment, as described above,uses the piezoelectric elements 130 and 132 producing oscillationshaving different frequencies and is designed to, as shown in FIG. 11,rotate the outer cylinder 111 in a direction as indicated by an arrow133 to scan an angular area 134 using the higher frequency piezoelectricelement 130 and an angular area 135 using the lower frequencypiezoelectric element 132. Specifically, an ultrasonogram of a nearbyportion of an object is derived by use of an ultrasonic wave having ahigher frequency, thereby increasing the resolution of theultrasonogram, while an ultrasonogram of a distance portion of theobject is derived by use of an ultrasonic wave having a lower frequency,thereby increasing the distance the ultrasonic wave travels.

The rotor motor 2D may also use more than two piezoelectric elementsproducing oscillations having different frequencies.

FIG. 12 shows a rotor motor 2E according to the sixth embodiment of theinvention which is different from the rotor motor 2 of the firstembodiment only in that a magnetroresistive element 400 is installed onthe chassis 111 which is magnetically responsive to the magnetic member122 to detect a neutral position of the outer cylinder 111 in swing ofthe rotary base 140 about the y-axis. Other arrangements are identical,and explanation thereof in detail will be omitted here.

FIG. 13(a) shows the waveform of an output signal of themagnetoresistive element 400 during a 360° rotation of the outercylinder 111 when the rotary base 140 is located at a swing angle ofzero (i.e., the neutral position). FIG. 13(b) shows the waveform of anoutput signal of the magnetoresistive element 400 during a 360° rotationof the outer cylinder 111 when the rotary base 140 is swung along theguide paths, as described in the first embodiment. When the swing angleof the rotary base 140 is zero (0° ), that is, when the rotary base 140is in the neutral position, a complete rotation of the outer cylinder111 causes the magnetic member 122 to pass the magnetoresistive element400 disposed on the chassis 11 one time, thereby resulting in, as shownin FIG. 13(a), a peak output 410 of the magnetoresistive element 400. Asthe magnetic member 122 approaches the magnetoresistive element 400, thevalue of the peak 410 becomes great. When the rotary base 140 is swungfrom the neutral position, the magnetic member 122 moves away from themagnetoresisitve element 400, so that no peak is, as shown in FIG.13(b), produced. The measurement of the neutral position of the rotarybase 140 is, thus, achieved by swinging the rotary base 140 andmonitoring the value of the peak of an output of the magnetoresistiveelement 400.

FIG. 14 shows a rotor motor 2F according to the seventh embodiment ofthe invention which is a modification of the sixth embodiment in whichthree magnetoresistive elements 401, 402, and 403 are so installed onthe chassis 11 as to face the magnetic member 122 of the first encoder120 used to detect the reference angular position of the outer cylinder111. Other arrangements are identical with those in the sixthembodiment, and explanation thereof in detail will be omitted here.

FIG. 15(a) shows waveforms of output signals of the magnetoresistiveelements 401, 402, and 403 during a 360° rotation of the outer cylinder111 when the rotary base 140 is located at a swing angle of zero (i.e.,the neutral position). 401A indicates the output of the magnetoresistiveelement 401. 402A indicates the output of the magentoresistive element402. 403A indicates the output of the magnetoresistive element 403. FIG.15(b) shows waveforms of output signals of the magnetoresistive elements401, 402, and 403 during a 360° rotation of the outer cylinder 111 whenthe rotary base 140 is swung toward the magnetoresistive element 401from the neutral position. 401B indicates the output of themagnetoresistive element 401. 402B indicates the output of themagentoresistive element 402. 403B indicates the output of themagnetoresistive element 403. FIG. 15(c) shows waveforms of outputsignals of the magnetoresistive elements 401, 402, and 403 during a 360°rotation of the outer cylinder 111 when the rotary base 140 is swungtoward the magnetoresistive element 403 from the neutral position. 401Cindicates the output of the magnetoresistive element 401. 402C indicatesthe output of the magentoresistive element 402. 403C indicates theoutput of the magnetoresistive element 403.

In operation, the direction of rotation of the outer cylinder 111 isdetermined by monitoring the levels of peaks of the outputs from themagnetoresistive elements 401, 402, and 403. Specifically, when thelevel of the peak of the output from the magnetoresistive element 401is, as indicated by 401B in FIG. 15(b), greater than those of themagentoresistive elements 402 and 403, it is determined that the rotarybase 140 being swinging close to the magnetoresistive element 401 fromthe neutral position. Alternatively, when the level of the peak of theoutput from the magnetoresistive element 403 is, as indicated by 403C inFIG. 15(c), greater than those of the magentoresistive elements 401 and402, it is determined that the rotary base 140 being swinging close tothe magnetoresistive element 403 from the neutral position. When thelevel of the peak of the output from the magnetoresistive element 402is, as indicated by 401A in FIG. 15(a), the greatest of the three, andthe levels of the outputs of the magnetoresistive elements 401 and 403are equal to each other, it is determined that the rotary base 140 is inthe neutral position.

While the present invention has been disclosed in terms of the preferredembodiments in order to facilitate better understanding thereof, itshould be appreciated that the invention can be embodied in various wayswithout departing from the principle of the invention. Therefore, theinvention should be understood to include all possible embodiments andmodifications to the shown embodiments which can be embodied withoutdeparting from the principle of the invention as set forth in theappended claims.

What is claimed is:
 1. An ultrasonic probe comprising: a piezoelectricelement emitting an ultrasonic wave and receiving an echo thereof, saidpiezoelectric element converting the echo into an electric signal; aholding member holding said piezoelectric element; a rotating mechanismrotating said holding member about a first axis; said rotating mechanismincluding a holding member angular position measuring encoder designedto measure an angular position of said holding member; said holdingmember angular position measuring encoder including a first encoder unitand a second encoder unit each of which is made of a magnetic member anda magnetoresistive element, the first encoder unit being designed tomeasure a change in angular position of said holding member by rotationabout the first axis, the second encoder unit being designed to measurea preselected reference angular position of said holding member; arotary base supporting said rotating mechanism; a fixed chassissupporting said rotary base so as to allow said rotary base to swingabout a second axis extending in a direction different from the firstaxis; and a swinging mechanism swinging said rotary base.
 2. Anultrasonic probe comprising: a piezoelectric element emitting anultrasonic wave and receiving an echo thereof, said piezoelectricelement converting the echo into an electric signal; a holding memberholding said piezoelectric element; a rotating mechanism rotating saidholding member about the first axis; a rotary base supporting saidrotating mechanism; a fixed chassis supporting said rotary base so as toallow said rotary base to swing about a second axis extending in adirection different from the first axis; and a swinging mechanismswinging said rotary base; said rotating, mechanism including a -holdingmember rotating electric motor rotating said holding member made of arotary cylinder, a conductive cylinder arranged in alignment of acentral axis with a central axis of the rotary cylinder, and aconductive brush installed on said rotary base in contact with theconductive cylinder.
 3. An ultrasonic probe comprising: a piezoelectricelement emitting an ultrasonic wave and receiving an echo thereof, saidpiezoelectric element converting the echo into an electric signal; aholding member holding said piezoelectric element; a rotating mechanismrotating said holding member about the first axis; a rotary basesupporting said rotating mechanism; a fixed chassis supporting saidrotary base so as to allow said rotary base to swing about a second axisextending in a direction different from the first axis; and a swingingmechanism swinging said rotary base; said rotating mechanism including aholding member rotating electric motor rotating said holding member madeof a rotary cylinder, a first coil installed on the rotary cylinder, anda second coil installed on said rotary base so as to face the firstcoil, said first coil being responsive to a change in magnetic flux ofsaid second coil to produce an electric signal for energizing saidpiezoelectric element.
 4. An ultrasonic probe comprising: apiezoelectric element emitting an ultrasonic wave and receiving an echothereof, said piezoelectric element converting the echo into an electricsignal; a holding member holding said piezoelectric element; a rotatingmechanism rotating said holding member about the first axis; a rotarybase supporting said rotating mechanism; a fixed chassis supporting saidrotary base so as to allow said rotary base to swing about a second axisextending in a direction different from the first axis; and a swingingmechanism swinging said rotary base; said swinging mechanism including arotary base swinging electric motor, a motor angular position measuringencoder measuring an angular position of said rotary base swingingelectric motor, and a gear train transmitting output torque of saidrotary base swinging electric motor to said rotary base to swing saidrotary base.
 5. An ultrasonic probe comprising: a piezoelectric elementemitting an ultrasonic wave and receiving an echo thereof, saidpiezoelectric element converting the echo into an electric signal; aholding member holding said piezoelectric element; a rotating mechanismrotating said holding member about the first axis; a rotary basesupporting said rotating mechanism; a fixed chassis supporting saidrotary base so as to allow said rotary base to swing about a second axisextending in a direction different from the first axis; and a swingingmechanism swinging said rotary base; said swinging mechanism including avoice coil motor and a rotary base angular position measuring encoderwhich measures an angular position of said rotary base, the voice coilmotor being implemented by a magnet installed on one of said rotary baseand said chassis and an electric coil installed on the other of saidrotary base and said chassis.
 6. An ultrasonic probe as set forth inclaim 5, further comprising a holding mechanism designed to hold saidrotary base on said chassis.
 7. An ultrasonic probe comprising: apiezoelectric element emitting an ultrasonic wave and receiving an echothereof, said piezoelectric element converting the echo into an electricsignal; a holding member holding said piezoelectric element; a rotatingmechanism rotating said holding member about the first axis; a rotarybase supporting said rotating mechanism; a fixed chassis supporting saidrotary base so as to allow said rotary base to swing about a second axisextending in a direction different-from the first axis; and a swingingmechanism swinging said rotary base; and a second piezoelectric elementinstalled on said holding member which produces an ultrasonic wavehaving a frequency different from that produced by said piezoelectricelement.
 8. An ultrasonic probe as set forth in claim 3, furthercomprising a magnetoresistive element responsive to a change in magneticflux produced by the magnetic member of the second encoder to provide asignal indicative of a neutral position of said holding member inswinging motion of said holding member.
 9. An ultrasonic probe as setforth in claim 3, further comprising an array of magnetoresistiveelements installed on said chassis, each of the magnetoresistive elementbeing responsive to a change in magnetic flux produced by the magneticmember of the second encoder to provide a signal indicative thereof.